Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$247.91	10.426%	$273.7571	$273.76	$273.75	$273.80
Purchase #2	$41.68	13.730%	$47.4027	$47.40	$47.40	$47.40
Purchase #3	$82.87	8.714%	$90.0913	$90.09	$90.10	$90.10
Purchase #4	$113.59	13.432%	$128.8474	$128.85	$128.85	$128.80
Purchase #5	$200.64	7.231%	$215.1483	$215.15	$215.15	$215.10
Purchase #6	$5.43	4.447%	$5.6715	$5.67	$5.65	$5.70
Purchase #7	$209.27	6.765%	$223.4271	$223.43	$223.45	$223.40
7 purchase totals =	$901.39		$984.3454	$984.35	$984.35	$984.30